Probe-based data collection system with adaptive mode of probing controlled by local sample properties

ABSTRACT

A method for testing an integrated circuit (IC) using a nanoprobe, by using a scanning electron microscope (SEM) to register the nanoprobe to an identified feature on the IC; navigating the nanoprobe to a region of interest; scanning the nanoprobe over the surface of the IC while reading data from the nanoprobe; when the data from the nanoprobe indicates that the nanoprobe traverse a feature of interest, decelerating the scanning speed of the nanoprobe and performing testing of the IC. The scanning can be done at a prescribed nanoprobe tip force, and during the step of decelerating the scanning speed, the method further includes increasing the nanoprobe tip force.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 61/838,744 filed on Jun. 24, 2013, and thedisclosure of which is hereby incorporated herein by reference in itsentirety.

BACKGROUND

1. Field of Invention

This invention is in the field of sample probing (including electrical)using scanning probe and nanoprobing systems.

2. Related Art

Nanoprobing (using scanning or point probing) is a very broad field ofanalytical science covering various types of electrical, mechanical,compositional and chemical physical characterization of nano-sizeobjects. Nanoelectronic devices and their components are examples ofsuch objects. Electrical probing of single transistors, memory bitcelland critical parts of integrated circuits (IC) is used widely to testperformance of newly designed IC and to correct potential problems ofthe specific IC design or/and overall technology.

To test the elements of an IC, the nanoprobes are made to physicallycontact the surface of the IC and to scan the surface of the IC. Thescanning can be used to generate topography image, capacitance image(dC/dV), etc. To generate those images, every pixel of the image isgenerated as the probe scan the surface at the same speed and with thesame force applied to the probe. However, there are circumstanceswherein certain areas of the scanning are not of interest for theparticular test, in which case there's no need for slow, high-resolutionscanning. In other cases, certain areas of the region of interest (ROI)may constitute a softer or more sensitive layer, such that less forceshould be applied. In yet other cases the probes should simply contactcertain elements without the need for scanning, e.g., to read electricalsignals in a point probing mode. Thus, there's a need for improvednanoprobing device and method for operating the nanoprobes, such thatthe above cases are taken into consideration.

SUMMARY

The following summary of the disclosure is included in order to providea basic understanding of some aspects and features of the invention.This summary is not an extensive overview of the invention and as suchit is not intended to particularly identify key or critical elements ofthe invention or to delineate the scope of the invention. Its solepurpose is to present some concepts of the invention in a simplifiedform as a prelude to the more detailed description that is presentedbelow.

Various disclosed embodiments utilize systems and methods wherein theprobe scanning speed and force are variable during the scanning of thesample. When the probes are scanning areas that are of no interest, thespeed can be increased until a new area of interest is reached, whereinthe speed is decreased. Similarly, when the probe is scanning asensitive area, or area of no interest, the force can be reduced, toprevent damage to the sensitive area and to reduce wear of the probes.For example, when the probes are scanning over an interlayer dielectric,the force should be reduced (to cause less sample damage and lessprobe-tip wear) and the speed should be increased (to provide higherthroughput, even at reduced resolution), since the dielectric area is ofno interest for the electrical testing).

In other embodiments, the probes are used to collect electrical dataand, therefore, need not scan the sample, but rather contact specificpoints on the device. In such cases, the probes' positions areregistered to the sample outside of the area of interest. Then, theprobes are moved blindly above the sample, i.e., without physicalcontact with the sample, to the ROI using a priori knowledge of thecircuit layout (e.g., from CAD file). When the probes are in the properposition above the specific points, the probes are moved down so as to“land” on the appropriate points.

According to disclosed embodiments, an adaptive (i.e., variable) mode ofprobe motion is executed during sample probing. The adaptive modeoperates the probes to test the sample using a combination of any of thefollowing modes of motion: hopping, contact scanning, non-contactscanning, taping, scanning with variable feedback type, scanning atdifferent speeds, scanning at different force, scanning at differentamplitude of oscillation, etc. The specific mode of motion is selectedaccording to the local properties of the sample, which may be known apriory (for example from CAD information) or/and assessed in real time(for example from robust high signal-to-noise ratio electrical ormechanical probe signal).

The embodiments are beneficial as data quality improvement achievedusing an optimized probe-sample interaction adjusted for and dependenton (1) local properties of the sample and also (2) type of measurementto be done at the particular location. The embodiments are alsobeneficial for preserving of the sample and probe(s) for repeatable andprecise measurements on the stable sample-probe system, by avoidingunnecessary wear of the probe tips.

DRAWINGS

Other aspects and features of the invention would be apparent from thedetailed description, which is made with reference to the followingdrawings. It should be mentioned that the detailed description and thedrawings provide various non-limiting examples of various embodiments ofthe invention, which is defined by the appended claims.

The accompanying drawings, which are incorporated in and constitute apart of this specification, exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the invention. The drawings are intended toillustrate major features of the exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of actualembodiments nor relative dimensions of the depicted elements, and arenot drawn to scale.

FIG. 1 illustrates a probing system according to one embodiment;

FIG. 2 illustrates various probing modes according to an embodiment;

FIG. 3 illustrates registration and blind move according to oneembodiment.

DETAILED DESCRIPTION

Various embodiments will be described below to achieve the benefits ofthe invention. Some of the benefits include the following.

(1) Scanning a sample with physical contact of the probe tip can damagethe sample. For certain locations or parts of the sample, physicalcontact with prescribed force or pressure is required in order to obtainthe needed data. However, there are cases where some parts of the sampleare not that critical for the tests. In such cases, disclosedembodiments avoid damage caused by contact mode of scanning.

(2) The prober throughput and data quality can be optimized usinghigh-speed low-pressure or non-contact motion over areas of no-interest,and slow increased-pressure contact motion (optimized) or even a fullstop at sites of interest (for the period of time needed to achievedesired quality of data).

(3) The probe tip lifetime can be improved by avoiding high pressureand/or contact with the sample when not needed. The probe tip can bemade to “fly” over areas of no-interest at safe height above thesample's surface.

(4) When high-integrity electrical data needs to be collected from thesample, the data quality can be improved by placing the probe incomplete stop and full contact during data acquisition.

The above benefits are achieved by the following embodiments.

FIG. 1 illustrates a nanoprober system according to one embodiments ofthe invention. A sample 105, such as a microchip, is placed on an x-y-zstage 110. The stage 110 may be controlled by controller 130, or by aseparate stage controller. A nanoprober 115 includes an actuator 113,for example, a piezoelectric actuator, and a probe tip 117. The probetip 117 can be placed and/or moved across the surface of sample 105, bythe motion of the actuator 113. The actuator 113 is controlled bycontroller 130. Also, if data is collected from the probe tip 117, thedata is sent to the controller 130. Additionally, the motion of the tip117 can be sensed by illuminating the tip using laser 120 and sensingthe reflection using optical sensor 125. The illumination and opticalsensing can be controlled using the same controller 130. The opticalsensing is especially beneficial for sensing z-motion, i.e., changes ofelevation, amplitude and frequency of oscillation of the probe tip 117,so as to create topography map, surface potential map, capacitance map,etc. More information about this technique can be found in U.S. Pat. No.5,267,471, the disclosure of which is incorporated herein by referencein its entirety. While in FIG. 1 only one nanoprober 115 is illustrated,in the various embodiments described, a plurality of nanoprobers is usedto simultaneously test the sample. In one example, eight nanoprober tipsare controlled simultaneously by the controller 130.

FIG. 2 illustrates an embodiment of a method for adoptive scanning theprobe tips 117, such as illustrated in FIG. 1. A cross-section of partof sample 105 is illustrated at the bottom of FIG. 2. In this example,the sample 105 has metal areas 102 and areas of interlayer dielectric104. Scanning and time progresses from left to right and is shown on thex-axis of the plot in the upper part of FIG. 2. The speed (shown asdotted line) and the force of scanning (shown by double-dotted line) arecontrolled by the controller according to the probing signal (shown insolid line), read from the prober. Speed, force and probe signals areplotted over the Y-axis. For example, if checking the probe signal forconductivity or capacitive signal (dC/dV), when the probe tip is overthe dielectric region 104, i.e., on the left side of the sample 105, noor low-level signal is read from the prober. During this time, theprober is operated at high speed and low pressure mode. Once thehigh-level signal is detected (solid-line plot), it indicates that theprobe tip is traversing over a conductive region 102. The speed is thenslowed down until it the prober reaches full stop. Meanwhile, the forceis increased and data acquisition starts. The force can be measured by,e.g., stress or strain sensors measuring the bending of the probe tipand feeding the signal to the controller 130. Once proper probingsignal-to-noise level is achieved, data acquisition stops and scanningis continued at the high speed and with low (or zero) force of contact.The scanning proceeds in this mode until the next indication of metal orhigh signal region is reached, wherein the process repeats.

According to another example, the changes of scanning speed and force ofprobe-sample interaction is triggered by CAD information from a CAD file140 (FIG. 1). Moreover, the CAD data file can be used together with thecapacitance (dC/dV) or any other signal. For example, when the CAD dataindicates that the probe tip is over regions representing interlayerdielectric, these regions could be skipped all together (hopped over) orscanned with the fastest speed and the lowest contact force. Then, priorto reaching an area indicated by the CAD data to correspond to aconductive (or other feature of interest), the speed is slowed and theforce may or may not be increased, and the scan is continued whilereading the capacitance or other data from the prober. Once a pre-setthreshold of capacitance dC/dV signal is detected, the probe scanning iscontrolled according to the speed/force signals shown in FIG. 2. Thedata acquisition continues until proper signal-to-noise ratio isachieved, and then scanning at the high speed and low (possibly zero forhopping) force is continued towards the next feature, as indicated bythe CAD data. Thus, according to this embodiment, three modes can beused: hopping (no contact, zero force, and highest speed), highspeed/low force, and deceleration to a stop while increasing force to amaximum set point.

According to one embodiment, the probe to sample registration isconducted outside of the area of interest. The probe can be registeredto the sample using imaging, e.g., scanning electron microscope (SEM)imaging. The sample may also be registered to a CAD pattern, if it is tobe used for hopping/scanning modes. Once the probes are registered toSEM image and CAD pattern, “blind moves” to the points of interestfollowed by data acquisition could be made. The blind moves can beassisted using the CAD data for navigation, similar to a GPS (globalposition system). Depending on the amount of probe vs. stage drift,periodic probe to sample re-registration and correction may be needed.

FIG. 3 illustrates the use of SEM for registration, and then performingblind motion to the ROI using, e.g., CAD data. In FIG. 3, a section ofsample 105 is illustrated, wherein two particular sections aredelineated, an ROI (which may be sensitive device) and a non-ROI (whichmay be an alignment target or a feature of no interest). Within thedelineated areas part of the surface is dielectric 104, and parts arefeatures of interest 102, e.g., metal contacts, metal lines, etc. Thenon-ROI section is first imaged using SEM, and the probe tips 117 arelanded on the sample. Tip position for each probe is registered to thesample SEM image and the corresponding CAD pattern. Since thisdelineated area is not of interest, it can be exposed to e-beam of theSEM. However, in order not to disturb or damage the ROI, no e-beam isscanned over the ROI, such that no SEM image of the ROI is produced.Instead, the system uses information from CAD design or other navigationaid, to blindly move each tip to a selected feature of interest in theROI and land the tips on the selected features of interest in the ROI.According to one example, the move is followed by data acquisition withzero probe speed and optimal force of contact, followed by blind move tothe next area of interest or back to the registration no-interest area.Moves are done using CAD or/and other navigation data. During everyreturn to the registration point, probe to sample position isre-adjusted. The later will reduce probe to sample registrationinaccuracy caused by slow relative drift of the two (for example bythermal drift).

Although electrical nanoprobing was provided as an example of adaptiveprobing, the same approach can be used for other types of probing.According to one example, tip-enhanced optical circuit analysis (TE OCA)can be done using so-called backside approach. With this approach Siwafer is thinned to about 100 nm thickness. IC tester is connected tothe IC from the front side in a normal manner. Standard IC tests areconducted on the thinned chip. Electro-optical emission from operatingFET p/n junctions is usually detected using high-resolution highnumerical aperture optics (www.dcg.systems.com). In this examplenanoprober tip is brought to the ROI from the back side of the wafer.

The metal probe is acting as an antenna which amplifies electro-magnetic(EM) field in the probe apex proximity (the effect is similar to thetip-enhanced Raman spectroscopy or TERS). As a result, at any moment oftime low-resolution optics (placed at the back side of the wafer)collects photons mostly from the probe apex proximity (where EM field isamplified). Once collected signal is synchronized with the probeposition, the high-resolution map of electro-optical emission isconstructed.

According to another embodiment of this example nanoprober tip is movingparallel to the backside of the wafer with variable speed and atvariable distance between the sample surface and the probe. Suchadoptive (speed and distance) probe motion will improve throughput,signal-to-noise and lateral resolution of the TE OCA method.

In another example the front side TE optical spectroscopy (Raman orfluorescence) can be used for high resolution and throughput defectanalysis. A large laser spot is used to irradiate sample. The probe isscanned over ROI with low (nanometer) scale topography. Low resolutionoptics is used for collection of scattered (Raman or/and fluorescence)photon. The method spatial resolution is defined by the size of theprobe apex and not by the resolution of photon collection optics.Throughput of the method is usually very low since long per pixel timeis used to collect sufficient number of scattered photons. If one triesto collect spectral map of the scattered photons the data collectiontime becomes almost impractical. Adoptive scanning helps to reduce thedata acquisition time. Tip is scanned at high speed collectingmonochrome signal with relatively poor signal-to-noise. Once suspicious(monochrome) signal is detected at certain locations the probe stops atthe spot and tool collects high signal-to-noise spectral data.

1. An apparatus for performing sample probing, comprising: a stage forsupporting a sample; an actuator activating a prober to collect datafrom the sample; a controller collecting data signals from the proberand sending actuating signals to the actuator, the controllerpreprogrammed to vary the actuating signals according to the datasignals received from the prober.
 2. The apparatus of claim 1, whereinthe controller is further preprogrammed to read a CAD design datacorresponding to the sample, and to further control the actuatingsignals according to the CAD design data.
 3. The apparatus of claim 1,wherein the controller is preprogrammed to vary at least one of scanningspeed, amplitude of probe oscillation, gap between the probe and samplesurface and probe contact force of the actuating signals, according tothe data signals.
 4. The apparatus of claim 2, wherein the controller ispreprogrammed to vary at least scanning speed and probe contact force ofthe actuating signals, according to the data signals.
 5. The apparatusof claim 1, wherein the controller is preprogrammed to vary scanningspeed and probe contact force of the actuating signals by switchingbetween at least a first and a second scanning modes, wherein the secondscanning mode comprises slower speed and higher force than the firstscanning mode.
 6. The apparatus of claim 5, wherein the second scanningmode further comprises a decelerating speed to a halt.
 7. The apparatusof claim 1, wherein the controller is further preprogrammed to registerthe prober to an image obtained by a scanning electron microscope.
 8. Amethod of performing sample probing using a prober having a probe tip,comprising the steps of: scanning the probe tip over the surface of thesample using a first speed and a first tip force, while reading signalsobtained from the prober; when the signals indicate that the probe tiptraverses a feature of interest, decelerating the probe tip from thefirst speed and increasing the tip force, and thereafter performingtests on the sample using the probe tip; when tests completed,accelerating the probe tip to the first speed and decreasing the forceto the first tip force.
 9. The method of claim 8, wherein the step ofdecelerating is performed to cause the probe tip to stop scanning, priorto performing tests.
 10. The method of claim 8, further comprising thesteps: registering the probe tip to the sample outside of an area ofinterest (ROI); and, blindly moving the probe tip to the area ofinterest.
 11. The method of claim 10, wherein the step of registeringthe probe is performed using the first speed.
 12. The method of claim10, wherein blindly moving is performed by moving the probe tip withoutcontacting the sample.
 13. The method of claim 10, wherein blindlymoving is performed using the first speed and first force.
 14. Themethod of claim 8, further comprising assessing test data quality priorto accelerating the probe tip.
 15. A method for testing an integratedcircuit (IC) using a nanoprobe, comprising: using a scanning electronmicroscope (SEM) to register the nanoprobe to an identified feature onthe IC; navigating the nanoprobe to a region of interest; scanning thenanoprobe over the surface of the IC while reading data from thenanoprobe; when the data from the nanoprobe indicates that the nanoprobetraverse a feature of interest, decelerating the scanning speed of thenanoprobe and performing testing of the IC.
 16. The method of claim 15,wherein the step of decelerating the scanning speed comprisesdecelerating to a halt.
 17. The method of claim 15, further comprisesincreasing tip force of the nanoprober while decelerating the scanningspeed.
 18. The method of claim 17, further comprising detecting signalto noise ratio of the data from the nanoprober and ceasing to increasethe probe tip force when the signal to noise ratio reaches a presetthreshold.
 19. The method of claim 15, wherein the step of navigatingthe nanoprobe to a region of interest comprises moving the nanoprobewith the nanoprobe hovering above the surface of the sample.
 20. Themethod of claim 15, wherein the step of scanning the nanoprobe comprisesscanning at a prescribed nanoprobe tip force, and wherein during thestep of decelerating the scanning speed, the method further comprisesincreasing the nanoprobe tip force.